John says he sees another “great and marvelous sign,” the third such description in the book (cf. 12:1 and 12:3). The sign, in this case, is the last set of seven angels. These are the last because “God’s wrath is completed.” God’s wrath is associated with Israel’s rebelliousness, but the prophets extend that wrath to the eschatological events (Isa 26:20, Ezek 7:19, 22:24, for example).
In Revelation, God’s wrath is a featured attribute of God. This is a righteous wrath, and is to a large extent anthropomorphic. God’s anger is not at all like human wrath, he is justly punishing those who have offended his law. The wrath of God is nearly completed. This can be translated “has been accomplished,” meaning that with these final judgments the wrath which was begun in chapter 6 has run its course.
The doors to the heavenly temple are opened and seven angels appear with the final seven plagues. The description of this location is as the temple and the tent / tabernacle. The reference to the tent is likely to the tent of meeting, the place where Moses spoke face to face with the Lord, yet another allusion to events of the Exodus.
Temples with open doors were considered a “bad sign” in the ancient world. David Aune lists several sources indicating a temple door opening by themselves was a sign of God’s wrath (Revelation, 2:878). The whole temple is filled with the smoke of the glory of God. This is a theophany: God’s presence is about to come to earth to finish his wrath.
After announcing that the final wrath of God has begun, John witnesses yet another worship scene in heaven (15:2-4). This worship scene has elements from chapter 4-5, now familiar scenes of heavenly worship (sea of glass, martyrs worshiping, harps and singing). In this case the martyrs are identified as those who have overcome the beast and the number of his name. Presumably they have been martyred because they refused to take the mark of the beast.
The song they are singing is identified as the Song of Moses and the Song of the Lamb. The Song of Moses is found in Exodus 15:1-18, Deut. 31:30-32:43; and Psalm 90. The problem with the Song of Moses in this context is that there is no literary relationship between the song recorded in Revelation and the various versions of the Song of Moses in the Old Testament. Perhaps what follows is only the Song of the Lamb and the reader is assumed to know what the song of Moses is. More likely is that the context of the original song is what John wants to evoke. If you head someone hum a few notes of a famous song, the whole song comes to mind.
The Song of Moses is worship of God because he has overcome the enemies of Israel. In Exodus, God rescued his people out of Egypt and overcame the Egyptians and their gods. There are obvious connections between the following bowl judgments and Exodus. Just as he has done in the past, God is once again working to redeem his people from an oppressive and evil empire.